It is desirable to test the friction provided by a road surface, carriageway, runway or the like. A road, runway or other with poor friction is potentially dangerous to users. The friction provided by a surface may change over time, depending on the composition of the surface and the conditions or wear it has been exposed to. The amount of friction provided may vary at corners or near junctions as these areas may be subjected to greater loading by turning, braking or accelerating actions. Friction may also vary across the width of a carriageway. Therefore it is desirable to be able to monitor the frictional properties of a carriageway.
Known friction testers include vehicles with a braked tyre engaged with a surface to be tested.
US 2014/0202230 discloses a friction testing device with a first and second wheel, where the first and second wheels are connected by a transmission so that the first wheel and second wheel rotate at different (but related) speeds of rotation so that, when both wheels are engaged with a surface, one of the wheels slips over the surface.
WO 00/17024 discloses a friction measuring system with a test wheel connected to an electric motor. An accelerating or breaking force is applied to the test wheel to create slippage, and measurements are taken to determine road surface friction.
U.S. Pat. No. 3,948,080 discloses a device to test tyre traction by applying a driving or breaking force to a pneumatic tyre and resolving the resultant forces.
SU 1567917 discloses a test wheel attached to a vehicle. The test wheel can be raised and lowered from the surface of the road. The test wheel is driven in the opposite direction to the direction of travel of the vehicle and the speed of travel of the vehicle, and then is lowered onto the surface.